The new light camouflage on this prototype offers a more revealing look, and it's not hard to see the influence of the new GS and LS models.

These new photos also provide a more detailed look at the 2014 model's tail lights, clearly inspired by the recent LF-CC concept - rumoured to preview a new IS-based 'RC' coupe.

Expect the marque's new 'Spindle' grille design to dominate the face of the new midsizer, finalising a theme that began with the smaller CT hatch.

The profile of the new grille can be seen beneath the cladding on this test car, while the rear-end features the sharp bootlid edge seen on GS and LS.

This prototype’s wheelbase is similar to the current model, but the front overhang looks to have gained a few millimetres - likely to benefit pedestrian safety and aerodynamic efficiency.

Mechanical details remain unclear for now, though the existing V6-only (in Australia) range is likely to be expanded with an efficiency-boosting four-cylinder option, along with BMW-sourced diesel engines in some markets.

Also likely is a hybrid version, which could use a rear-wheel drive version of the 2.5 litre four-cylinder petrol engine and electric drivetrain used in the Toyota Camry Hybrid.

This configuration is rumoured to be in development also for an ultra-efficient GS 300h version of the larger GS sedan.

Watch for the new IS range - at least in sedan form - to appear at the Detroit Auto Show in January.